Cooling blanket with cooling capability

ABSTRACT

A cooling blanket to provide cooling capability may include a first sheet, a second sheet opposed to the first sheet, a cooling tube positioned between the first sheet and the second sheet to provide a path for cooling fluid and a acoustic refrigerator to cool the cooling fluid.

FIELD OF THE INVENTION

The present invention relates to a blanket and more particularly to a cooling blanket that may include cooling capabilities.

BACKGROUND

Blankets have been used extensively to provide heat and warmth for individuals particularly to be used on beds. However, there is a need for a device to provide cooling capability especially in warmer climates during the summer time. Air-conditioning has been used to provide cooling capabilities for an entire room or structure, but there is a large amount of energy/electricity that is needed to provide the necessary air-conditioning.

There is a need to provide cooling capabilities at a fraction of the cost of cooling an entire room or building.

Thermoacoustic engines (sometimes called “TA engines”) are thermoacoustic devices which use high-amplitude sound waves to pump heat from one place to another, or conversely use a heat difference to induce high-amplitude sound waves. In general, thermoacoustic engines can be divided into standing wave and travelling wave devices. These two types of thermoacoustics devices can again be divided into two thermodynamic classes, a prime mover (or simply heat engine), and a heat pump. The prime mover creates work using heat, whereas a heat pump creates or moves heat using work. Compared to vapor refrigerators, thermoacoustic refrigerators have no ozone-depleting or toxic coolant and few or no moving parts therefore require no dynamic sealing or lubrication

History

The history of thermoacoustic hot air engines started about 1887, when Lord Rayleigh discussed the possibility of pumping heat with sound. Little further research occurred until Rott's work in 1969.

A very simple thermoacoustic hot air engine is the Rijke tube that converts heat into acoustic energy. This device however uses natural convection.

Research in Thermoacoustics

Modern research and development of thermoacoustic systems is largely based upon the work of Rott (1980) and later Steven Garrett, and Greg Swift (1988), in which linear thermoacoustic models were developed to form a basic quantitative understanding, and numeric models for computation. Commercial interest has resulted in niche applications such as small to medium scale cryogenic applications.

Current Research

Orest Symko at University of Utah began a research project in 2005 called Thermal Acoustic Piezo Energy Conversion (TAPEC).

Score Ltd. was awarded £2M in March 2007 to research a cooking stove that will also deliver electricity and cooling using the Thermo-acoustic effect for use in developing countries.

Cool Sound Industries, Inc. is developing an air-conditioning system that uses thermoacoustic technology, with a focus on HVAC applications. The system is claimed to have high efficiency and low costs compared to competing refrigeration technologies, and uses no HFC, no HCFC, and no mechanical compressor.

Q-Drive, Inc. is also engaged in developing thermoacoustic devices for refrigeration, with a focus on cryogenic applications.

SUMMARY

A cooling blanket to provide cooling capability may include a first sheet, a second sheet opposed to the first sheet, a cooling tube positioned between the first sheet and the second sheet to provide a path for cooling fluid and a acoustic refrigerator to cool the cooling fluid.

The acoustic refrigerator may include a cold heat exchanger.

The acoustic refrigerator may include a hot heat exchanger.

The acoustic refrigerator may include a loudspeaker.

The acoustic refrigerator may include a stack of plates.

The cooling tube may include a pump.

The cooling tube may include a heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be understood by reference to the following description taken in conjunction with the accompanying drawings, in which, like reference numerals identify like elements, and in which:

FIG. 1 illustrates a thermoacoustic refrigerator of the present invention;

FIG. 2 illustrates a detail of the thermoacoustic refrigerator of the present invention;

FIG. 3 illustrates a diagram of temperature and pressure of the thermoacoustic refrigerator of the present invention

FIG. 4 illustrates a blanket with cooling capabilities of the present invention;

FIG. 5 illustrates a portion of the blanket with cooling capabilities of the present invention;

FIG. 6 illustrates a cross-section of the cooling blanket of the present invention.

DETAILED DESCRIPTION

A thermoacoustic device basically consists of heat exchangers, a resonator, and a stack (on standing wave devices) or regenerator (on travelling wave devices). Depending on the type of engine a driver or loudspeaker might be used as well to generate sound waves.

Consider a tube closed at both ends. Interference can occur between two waves traveling in opposite directions at certain frequencies. The interference causes resonance creating a standing wave. Resonance only occurs at certain frequencies called resonance frequencies, and these are mainly determined by the length of the resonator.

The stack is a part consisting of small parallel channels. When the stack is placed at a certain location in the resonator, while having a standing wave in the resonator, a temperature difference can be measured across the stack. By placing heat exchangers at each side of the stack, heat can be moved. The opposite is possible as well, by creating a temperature difference across the stack, a sound wave can be induced. The first example is a simple heat pump, while the second is a prime mover.

Heat Pumping

To be able to create or move heat, work must be done, and the acoustic power provides this work. When a stack is placed inside a resonator a pressure drop occurs. Interference between the incoming and reflected wave is now imperfect since there is a difference in amplitude causing the standing wave to travel little, giving the wave acoustic power.

In the acoustic wave, parcels of gas adiabatically compress and expand. Pressure and temperature change simultaneously; when pressure reaches a maximum or minimum, so does the temperature. Heat pumping along a stack in a standing wave device can now be described using the Brayton cycle.

Below is the counter-clockwise Brayton cycle consisting of four processes for a refrigerator when a parcel of gas is followed between two plates of a stack.

-   -   1. Adiabatic compression of the gas. When a parcel of gas is         displaced from its rightmost position to its leftmost position,         the parcel is adiabatic compressed and thus the temperature         increases. At the leftmost position the parcel now has a higher         temperature than the warm plate.     -   2. Isobaric heat transfer. The parcel's temperature is higher         than that of the plate causing it to transfer heat to the plate         at constant pressure losing temperature.     -   3. Adiabatic expansion of the gas. The gas is displaced back         from the leftmost position to the rightmost position and due to         adiabatic expansion the gas is cooled to a temperature lower         than that of the cold plate.     -   4. Isobaric heat transfer. The parcel's temperature is now lower         than that of the plate causing heat to be transferred from the         cold plate to the gas at a constant pressure, increasing the         parcel's temperature back to its original value.

Travelling wave devices can be described using the Stirling cycle.

Temperature Gradient

An engine and heat pump both typically use a stack and heat exchangers. The boundary between a prime mover and heat pump is given by the temperature gradient operator, which is the mean temperature gradient divided by the critical temperature gradient.

$I = \frac{\nabla T_{m}}{\nabla T_{crit}}$

The mean temperature gradient is the temperature difference across the stack divided by the length of the stack.

${\nabla T_{m}} = \frac{\Delta \; T_{m}}{\Delta \; x_{stack}}$

The critical temperature gradient is a value depending on certain characteristics of the device like frequency, cross-sectional area and gas properties.

If the temperature gradient operator exceeds one, the mean temperature gradient is larger than the critical temperature gradient and the stack operates as a prime mover. If the temperature gradient operator is less than one, the mean temperature gradient is smaller than the critical gradient and the stack operates as a heat pump.

Theoretical Efficiency

In thermodynamics the highest achievable efficiency is the Carnot efficiency. The efficiency of thermoacoustic engines can be compared to Carnot efficiency using the temperature gradient operator.

The efficiency of a thermoacoustic engine is given by

$\eta = \frac{\eta_{c}}{I}$

The coefficient of performance of a thermoacoustic heat pump is given by

COP=I·COP _(c)

Derivations

Using the Navier-Stokes equations for fluids, Rott was able to derive equations specific for thermoacoustics. Swift continued with these equations, deriving expressions for the acoustic power in thermoacoustic devices.

Efficiency in Practice

The most efficient thermoacoustic devices built to date have an efficiency approaching 40% of the Carnot limit, or about 20% to 30% overall (depending on the heat engine temperatures).

Higher hot-end temperatures may be possible with thermoacoustic devices because there are no moving parts, thus allowing the Carnot efficiency to be higher. This may partially offset their lower efficiency, compared to conventional heat engines, as a percentage of Carnot.

The ideal Stirling cycle, approximated by travelling wave devices, is inherently more efficient than the ideal Brayton cycle, approximated by standing wave devices. However, the narrower pores required to give good thermal contact in a travelling wave regenerator, as compared to a standing wave stack which requires deliberately imperfect thermal contact, also gives rise to greater frictional losses, reducing the efficiency of a practical engine. The toroidal geometry often used in travelling wave devices, but not required for standing wave devices, can also give rise to losses due to Gedeon streaming around the loop.

FIG. 1 illustrates a thermal acoustic refrigerator 101 which may be electronically driven by a radically modified loudspeaker 103 to maintain a standing sound wave 105 which may be input to the loudspeaker 103 in an inert gas in a resonator 107. The sound wave 105 interacts with an array of parallel solid plates 109 referred to collectively as a stack 111. A cold heat exchanger 113 may be positioned at one end of the stack 111, and a hot heat exchanger 115 may be positioned at an opposing end of the stack 111. The resulting refrigeration can be understood by examining a typical small element of gas 117 between the plates 119 of the stack 111. As the gas 117 oscillates back and forth because of the effect from the standing sound wave, the element of gas 117 changes in temperature. Much of the temperature change comes from compression and expansion of the gas 117 by the sound pressure (as always in a sound wave), and the rest of the temperature change is a consequence of heat transfer between the gas 117 and the stack 111. In the example shown, the length of the resonator may be one fourth the wavelength of the sound produced by the speaker 103, so all the elements of gas 117 are compressed and heated as the gas 117 move to the right, and the elements of the gas 117 are expanded and cooled as they moved to the left. Thus each element of gas 117 goes through a thermodynamic cycle as shown in FIG. 3 in which the element of gas 117 is compressed and is heated; the element of gas 117 rejects heat at the right end of its range of oscillation; the element of gas 117 is depressurized and cooled, and absorbs heat at the left end. Consequently, each element of gas moves a little heat from left to right, from cold to hot, during each cycle of the sound wave. The combination of the cycles of all the elements of gas 117 transports heat from the cold heat exchanger to the hot heat exchanger much as a bucket brigade transports water. The spacing between the plates 109 in the stack provides proper function: if the spacing is too narrow, the good thermal contact between the gas 117 and the stack 111 keeps the gas at nearly the same temperature as the stack 111, whereas if the spacing is too wide, much of the gas 117 is in a poor thermal contact with the stack 111 and does not transfer heat effectively to and from the stack 111.

FIG. 2 illustrates a detail of a first plate 109 of the stack 111 and a second plate 109 of the stack 111, and illustrates the oscillation of the element of gas 117 between the cold heat exchanger 113 and the hot heat exchanger 115.

FIG. 4 illustrates the cooling blanket 100 of the present invention which may include a cooling tube 201 which may be filled with a cooling fluid such as anti-freeze to conduct the heat from the cooling blanket 100. The cooling tube may be formed into an array 205, and the cooling blanket 100 may include the thermal acoustic refrigerator 101 as illustrated in FIG. 1. The thermal acoustic refrigerator 101 may include an input tube 207 and an output tube 209 to input the fluid from the cooling tube 201 to the cold heat exchanger 113 and to output the fluid to the cooling tube 201 from the cold heat exchanger 113 respectively.

The input tube 207 and the output tube 209 are connected to a heat exchanger 211 as shown in FIG. 5 which may be positioned within the cooling tube 201 in order to cool the fluid to remove the heat from the cooling blanket 100 within the cooling tube 201.

FIG. 5 illustrates a connector 215 to connect the cooling tube 201 and may include a fluid pump 217 to circulate or pump the fluid to the cooling blanket 100 within the cooling tube 201 and may include an internal temperature sensor 219 to measure temperature.

FIG. 4 additionally illustrates that a power cord 221 may be connected to the acoustic refrigerator 101 to supply power to the acoustic refrigerator 101 and additionally illustrates an external temperature sensor 223 to measure the external temperature to the acoustic refrigerator 101.

FIG. 6 illustrates a cross-section of the cooling blanket 100 of the present invention and illustrates the cooling tube 201 positioned between a first sheet 202 and a second sheet 203.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed. 

1) A cooling blanket to provide cooling capability, comprising: a first sheet: a second sheet opposed to the first sheet; a cooling tube positioned between the first sheet and the second sheet to provide a path for cooling fluid; a acoustic refrigerator to cool the cooling fluid. 2) A cooling blanket to provide cooling capability as in claim 1, wherein the acoustic refrigerator includes a cold heat exchanger. 3) A cooling blanket to provide cooling capability as in claim 1, wherein the acoustic refrigerator includes a hot heat exchanger. 4) A cooling blanket to provide cooling capability as in claim 1, where in the acoustic refrigerator includes a loudspeaker. 5) A cooling blanket to provide cooling capability as in claim 1, wherein the acoustic refrigerator includes a stack of plates. 6) A cooling blanket to provide cooling capability as in claim 1, wherein the cooling tube includes a pump. 7) A cooling blanket to provide cooling capability as in claim 1, wherein the cooling tube includes a heat exchanger. 8) A cooling blanket to provide cooling capability as in claim 1, where in the cooling tube includes a temperature sensor. 